U.S. patent number 5,364,231 [Application Number 07/994,741] was granted by the patent office on 1994-11-15 for full authority propeller pitch control.
This patent grant is currently assigned to AlliedSignal Inc.. Invention is credited to Christopher D. Eick, Paul J. Powers, John R. Williamson.
United States Patent |
5,364,231 |
Eick , et al. |
November 15, 1994 |
Full authority propeller pitch control
Abstract
A control for a hydraulic propeller pitch actuator includes a
low power pilot valve responsive to digital electronic input
signals to control movement of a hydraulic servomotor driving a
higher power servovalve. Negative feedback motion is delivered from
the servomotor to both the pilot valve and the servovalve.
Inventors: |
Eick; Christopher D. (Phoenix,
AZ), Powers; Paul J. (Glendale, AZ), Williamson; John
R. (Scottsdale, AZ) |
Assignee: |
AlliedSignal Inc. (Morris
Township, Morris County, NJ)
|
Family
ID: |
25541002 |
Appl.
No.: |
07/994,741 |
Filed: |
December 22, 1992 |
Current U.S.
Class: |
416/157R; 416/48;
91/433; 91/449; 91/461 |
Current CPC
Class: |
B64C
11/38 (20130101) |
Current International
Class: |
B64C
11/00 (20060101); B64C 11/38 (20060101); B64C
011/40 () |
Field of
Search: |
;416/47,48,156,157R
;91/417R,433,449,461 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Look; Edward K.
Assistant Examiner: Verdier; Christopher
Attorney, Agent or Firm: Lester; Troy McFarland; James
W.
Claims
What is claimed is:
1. A variable pitch propeller assembly comprising:
a hub carrying a plurality of radially extending propeller blades,
said propeller blades mounted to rotate within said hub to adjust
blade pitch;
a propeller pitch piston positioned to translate within said hub
and connected to said propeller blades such that translation of
said propeller pitch piston rotates said propeller blades, said
propeller pitch piston having two opposing faces and biased on one
face by a spring and biased on the opposing face by a supply of
hydraulic fluid;
a tube secured to said propeller pitch piston to translate
therewith and to supply said hydraulic fluid;
a servo piston positioned to translate within a housing, said servo
piston dividing said housing into first and second chambers and
having a first opposing surface and a second opposing surface, said
first and second opposing surfaces being biased by hydraulic fluid
in said first and second chambers respectively;
a first bored shaft secured to translate with and extending from
said first opposing surface of said servo piston, said first bored
shaft extending from said housing to receive said tube such that
said tube is translatable relative to said first bored shaft;
a second bored shaft secured to translate with and extending from
said second opposing surface of said servo piston, said second
bored shaft extending out of said housing and containing a fluid
exhaust port; and
means for opening and covering said fluid exhaust port to a low
pressure return to adjust blade pitch.
2. The variable pitch propeller assembly of claim 1 wherein said
means for opening and covering said fluid exhaust port
includes:
a pilot valve member for covering said fluid exhaust port;
a motor for moving said pilot valve member; and
a controller for electronically operating said motor.
3. The variable pitch propeller assembly of claim 2 wherein said
pilot valve member is a pilot sleeve which circumferentially
surrounds said second bored shaft and translates thereon to open
and cover said fluid exhaust port.
4. The variable pitch propeller assembly of claim 3 wherein said
motor is a stepper motor.
5. The variable pitch propeller assembly of claim 1 wherein said
housing contains a supply port for receiving said supply of
hydraulic fluid into said first chamber.
6. The variable pitch propeller assembly of claim 5 further
including an orifice between said first and said second chambers to
allow said hydraulic fluid to flow from said first chamber to said
second chamber.
7. The variable pitch propeller assembly of claim 6, wherein said
orifice comprises a flow restricting passage extending through said
servo piston from said first to said second opposing surfaces
thereof.
8. The variable pitch propeller assembly of claim 6, wherein said
tube includes pressure and exhaust openings for respectively
connecting said propeller pitch piston with said supply of
hydraulic fluid and with said low pressure fluid return.
9. The variable pitch propeller assembly of claim 8, wherein said
first bored shaft includes a passage for delivering said supply of
hydraulic fluid to said pressure opening in said tube.
10. A control for a hydraulic propeller pitch actuator
comprising:
a power servo control valve for controlling flow of pressurized
hydraulic fluid to move said actuator in opposite directions;
a hydraulic servo motor movable in opposite directions and
mechanically connected to said servo control valve to move the
latter in opposite directions, said servo motor comprising a double
acting, hydraulic cylinder having a piston movable in opposite
directions, said piston connected to said servo control valve, said
cylinder having an exhaust port;
a low power pilot valve movable in opposite directions to control
pressurized fluid flow to drive said servo motor;
an input signal member, responsive to a low power, digital
electrical signal, mechanically connected to said pilot valve to
move the latter in opposite directions; and
means for defining a passage in fluid communication with said
actuator, said means including pressure and exhaust openings for
respectively connecting said actuator with pressurized fluid flow
and low pressure fluid return,
said servo control valve comprising a servo member movable in
opposite directions between a first position uncovering said
pressure opening while blocking said exhaust opening, and a second
position blocking said pressure opening while uncovering said
exhaust opening.
11. A control as set forth in claim 10, wherein said pilot valve
comprises a pilot member movable in opposite directions to open and
close said exhaust port.
12. A control as set forth in claim 11, wherein said exhaust port
is carried by and movable with said piston.
13. A control as set forth in claim 12, wherein said piston
includes a passage for carrying hydraulic fluid in said cylinder
from one side of the piston to the other, and a flow restricting
orifice in said passage, said exhaust port opening into said
cylinder on said other side of the piston.
14. A control as set forth in claim 13, wherein said input signal
member includes an electrical stepper motor operable to drive said
pilot member in opposite directions.
15. A control as set forth in claim 13, wherein said pilot member
is a sleeve shiftable in opposite directions to open and close said
exhaust port.
16. A control as set forth in claim 10, wherein said means for
defining a passage comprises a hollow, closed-end tube, said servo
member comprising a servo sleeve concentrically surrounding said
tube.
17. A control as set forth in claim 16, wherein one end of said
tube is received within a blind central bore in said piston, the
other end of said tube being affixed to and movable with said
actuator.
18. In a hydraulically operated variable pitch propeller actuator
of the type having an elongated tube for hydraulically
communicating with said actuator, one end of said tube secured to
said actuator and the other remote end disposed at a remote
location, said tube having spaced pressure and exhaust openings
near said remote end;
a housing having an internal bore;
a piston shiftable within said bore and dividing said bore into
separate first and second chambers on opposite sides of said
piston, said piston having first and second rods extending through
opposite ends of the housing, said first rod having a blind bore
receiving said remote end of the tube and cooperating therewith to
selectively cover and uncover said pressure and exhaust openings,
said first rod having a port for communicating said first chamber
with said blind bore, said second rod having an exhaust port and an
exhaust duct communicating said second chamber with said exhaust
port;
pressure supply means for delivering pressurized fluid flow to said
first and second chambers;
means for restricting rate of fluid flow from said supply means
into said second chamber; and
a pilot valve control member movable on said second rod to open and
close said exhaust port in the second rod.
Description
TECHNICAL FIELD
This invention relates to a propeller pitch control apparatus for
hydraulically operated variable pitch systems.
BACKGROUND OF THE INVENTION
Variable pitch propellers are employed in various applications
including turboprop engines. Turboprop engines have proven to be
desirable for aircraft because of high reliability and fuel
efficiency. A turboprop engine uses a gas turbine engine to provide
shaft power that rotates propeller blades. The blades provide
thrust to propel an aircraft. The thrust is varied by changing the
pitch of the blades. Forward thrust is achieved by rotating the
blades to a positive angle. At cruise, the blades are adjusted to
the intermediate positive position reducing engine torque and
saving fuel. During landings, the blades are rotated to a negative
angle to provide reverse thrust.
Propeller pitch for hydraulic applications is generally controlled
through three devices: a propeller pitch control, a propeller
governor, and a feathering valve. The propeller pitch control is
operated through the use of a power lever connected to pitch
control cam. The propeller pitch control allows the operator to
adjust the blade pitch during ground operation, typically between
the reverse and flight idle positions. The propeller governor
automatically adjusts the blade pitch, typically between the flight
idle and full power positions, to maintain a predetermined engine
speed. The governor uses flyweights to mechanically start a chain
reaction when engine speed increases above the predetermined speed
by opening a pilot valve plunger to increase blade pitch. This
increases engine load which will decrease engine speed back to the
predetermined speed. Finally, the feathering valve is essentially a
safety device to mechanically position the blade in the full
feather position during emergencies. The device is a mechanically
operated valve that, when opened, dumps the oil from the pitch
control system and adjusts the blades to the full feather
position.
Typically these systems operate a single acting propeller pitch
control piston. In a single acting pitch system, the hydraulic
fluid supplied by the prop governor or the pitch control is fed
through a beta tube to bias the propeller pitch control piston
against a spring. For a dual acting piston, two sources of oil are
typically controlled by the same types of mechanisms mentioned
above or other mechanical actuators connected to a spool type
valve. These oil supplies are typically fed to the pitch control
piston and react against each other to move the control piston.
While hydraulic pitch control systems are well known in the art and
have good reliability, they require heavy and complicated actuation
devices and associated linkages. Another problem is that the
governor requires speed error to adjust the blade pitch resulting
in fluctuations of blade pitch during transient conditions. Still
another problem is that the pitch control cam requires large
mechanical loads to operate.
Accordingly, a need exists for a pitch control device that can vary
blade pitch from the reverse position to the feather position with
a fewer number of components, that can control blade pitch during
flight with minimum speed error, and that does not require great
mechanical loads to operate.
SUMMARY OF THE INVENTION
The invention is an improvement to a hydraulically controlled
variable pitch control assembly that includes a follow-up servo
piston operated by a FADEC (Full Authority Digital Engine Control)
controlled stepper motor. Thus, the propeller pitch can be
controlled by the FADEC similar to existing fuel control systems by
using data from various sensors that indicate flight conditions and
engine speed. This will allow the FADEC to control the change in
propeller pitch through the follow-up servo piston, and thus,
greatly decrease the overall system weight by removing the
propeller governor, the pitch control and the feathering valve. The
present invention also eliminates fluctuations during transient
conditions attributed to the flyweights in the propeller governor
and removes the mechanical loads associated with the pitch control
cam.
Accordingly, it is an important object of the present invention to
provide a highly simplified propeller pitch control system directly
responsive to low power electrical control signals as may be
generated by a full authority digital engine control. The control
signals control opposite directions of motion of a hydraulic
servomotor which mechanically-positions a hydraulic power servo
control valve. Movement of the power servo control valve then ports
fluid in and out of the propeller pitch actuator.
These and other objects and advantages of the present invention are
specifically set forth in or will become apparent from the
following detailed description of a preferred embodiment of the
invention, when read in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is a perspective view of a turboprop engine employing a
pitch control device according to the present invention.
FIG. 2A is a cross-sectional view of a follow-up servo piston
propeller pitch controller according to the present invention.
FIG. 2B is a perspective cutaway of a single action propeller pitch
control piston operated by the apparatus in FIG. 2A.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings, FIG. 1 shows a turboprop engine 10
including a core engine 12 and a variable pitch propeller assembly
15. The core engine 12 is comprised of an air inlet 20, a
compressor section (not shown), a combustor section (not shown),
and a turbine section (not shown), all assembled in a flow series
relation. Journaled to the forward end of the core engine 12 is the
variable pitch propeller assembly 15 comprising a plurality of
propeller blades 18 circumferentially disposed about and radially
extending from a propeller hub 16. In operation, the core engine 12
provides shaft power to the propeller assembly 15 by compressing
air in the compressor section, combusting the compressed air with
fuel in the combustor section and expanding the combustion products
in the turbine section to provide shaft power. The shaft power is
used to rotate the blades 18 about axis 17 to move ambient air and
provide thrust for an aircraft (not shown).
Referring to FIG. 2A, a full authority propeller pitch control 14
is comprised of a hydraulic servo motor in the form of a
double-acting, linear servo piston 40 that is translated within a
housing 60 by hydraulic fluid supplied from a pump 70 to opposing
chambers 62, 64. A low power pilot control valve, in the form of a
pilot sleeve 84, is responsive to a stepper motor 82 and a full
authority digital engine control (FADEC) 80 to control the movement
of the servo piston 40. Integral to the servo piston 40 is a first
bored rod or shaft 50 that extends through one side of the housing
60 and receives one end of a hollow beta tube 32 described in
greater detail below. The shaft 50 has a blind bore presenting a
chamber 63 communicating with chamber 62 through passage 52, and
has an end section 51 that has a smaller diameter that is
approximately equal to the diameter of the beta tube 32. The
diameter of end section 51 must be great enough to allow the beta
tube to slide relative thereto.
Extending from the opposite face of piston 40 is a second rod or
bored shaft 42 with a duct 58 extending to an exhaust port 56. A
hole 54 allows fluid to flow between duct 58 and chamber 64. Shafts
50 and 42 are sized such that the reaction area of piston 40
subject to the fluid pressure from chamber 64 is greater than the
area of piston 40 subject the opposing fluid pressure from chambers
62 and 63 combined.
The pump 70 continuously supplies the hydraulic fluid which can be
recirculated through a relief valve 72 if the pressure in the
housing 60 becomes too great. The hydraulic fluid from pump 70 is
supplied to chamber 62 through conduit 74. The fluid flows through
an orifice 66 in a flow restricting passage through piston 40, and
passes between chambers 62 and 64. The fluid dumps from the housing
60 into a low pressure return such as the sump of a surrounding
gearbox 73 (depicted by dashed lines for simplicity) through the
exhaust port 56. The fluid also exits to low pressure return from
the interior 34 of beta tube 32 through an opening 36. Pressurized
fluid is supplied into the interior 34 of tube 32 through opening
38. Reduced diameter land 51 acts as a power servo control valve in
covering and uncovering openings 36, 38 in their communications
with the low pressure return gearbox 73 and pressurized bore 63,
respectively.
FIG. 2B illustrates a conventional propeller pitch control actuator
19 as may be utilized in conjunction with the control contemplated
by the present invention. The blades 18 (only one shown in FIG. 2B)
are fixed to rotate with a rotating blade housing 27 about the hub
centerline 17. The blade 18 can also rotate or swivel within the
housing 27 about the blade pitch centerline 29 to change the blade
pitch. An eccentric roller 23 is attached to the blade 18 on the
periphery of the bottom of the blade 18 in offset relation to the
pitch axis of rotation 29, and is moved by a pitch control piston
21. The pitch control piston 21 slides in a back and forth motion
within the housing 27 moving the disk 23 to rotate blade 18. The
pitch control piston 21 is biased on one side by a spring 22 and on
the other by a chamber 24 that fills with hydraulic fluid. The
piston also contains a bore 28 carrying beta tube 32 that is firmly
secured to piston 21 to both rotate with the housing 27 and
translate with piston 21. The hydraulic fluid is supplied from the
beta tube interior 34 through a hole 30 to the piston bore 28 and
then through a hole 26 to the hydraulic chamber 24. The pitch
control piston 21 movement is thus dependent on the supply of
hydraulic fluid to chamber 24 to react against the spring 22.
In operation, the propeller variable pitch control 14 is in a
balanced or in a stationary state when the hydraulic exhausts 56
and 36 are partially covered by pilot valve sleeve 84 and the
control valve 51 respectively. Fluid flow into chamber 64 through
orifice 66 and subsequent discharge through port 56, maintains a
pressure in chamber 64 which is lower than that in chamber 62. In
this state, servo piston 40 is stationary because the product of
the associated pressure times exposed piston area in chamber 64, is
equal to the product of associated higher pressure times exposed
piston area in chambers 62 and 63. The pitch control piston 21 is
stationary because the product of pressure times area in chamber 24
is equal to the spring 22 force.
When changing blade pitch, a leftward movement of the pitch control
piston 21 as depicted in FIG. 2B positions the blade 18 at a more
positive pitch angle. In the preferred embodiment, the FADEC 80
increases blade pitch by signalling the motor 82 to move the pilot
control sleeve 84 in the leftward direction in FIG. 2A. This
exposes more of port 56 to the gearbox 73 and increases the flow
therethrough. The increased flow through hole 56 decreases the
pressure in chamber 64 because the area of opening of port 56 is
now greater than the cross-sectional area of orifice 66. The
pressure in chambers 62 and 63 then forces the servo piston 40 in
the leftward direction until the port 56 is again partially covered
by the pilot control sleeve 84. Once the port 56 is partially
covered again, the pressure in chamber 64 increases and the servo
piston 40 becomes stationary at the new location.
This leftward motion of servo piston 40 causes shaft rod 50 and
associated power servo control valve 51 to cover opening 38 and to
uncover opening 36. This allows rapid fluid dump from the beta tube
32 to the gearbox 73. The loss of hydraulic fluid from the beta
tube 32 decreases the hydraulic pressure in hydraulic chamber 24,
allowing spring 22 to push the pitch control piston 21 and the
attached beta tube 32 leftwardly until hole 36 is partially covered
and hole 38 is partially exposed again. Once the holes are
partially exposed again, the product of pressure and area in
chamber 24 again equals the force of spring 22, and piston 21
becomes stationary at the new location. As explained earlier, the
leftward movement of piston 21 moves disk 23 which rotates blade 18
into an increased blade pitch.
In emergency situations the blade 18 can be forced into a feather
position by dumping the hydraulic fluid from chamber 24 and
allowing the spring 22 to position the piston 21 in its furthest
leftward position. Spring 92 loads pilot sleeve 84 against stepper
motor 82.
In a similar manner, the FADEC 80 decreases blade pitch by
signalling the motor 82 to move the pilot sleeve 84 in the
rightward direction, further covering port 56. This movement
increases the pressure in chamber 64 to shift the servo piston 40
rightwardly until the port 56 is re-opened. The rightward motion of
servo piston 40 causes shaft 50 to further uncover opening 38 while
further covering the opening 36. This rapidly increases the amount
of hydraulic fluid entering the beta tube 32 which increases the
pressure in chamber 24. The hydraulic fluid shifts the pitch
control piston 21 and the beta tube 32 rightwardly until openings
38 and 36 are both partially covered again. The rightward movement
of the pitch control piston 21 also moves the disk 23 to decrease
the blade 18 pitch angle.
The FADEC 80 can be programmed to adjust blade pitch similarly to
when controlling fuel supplies, by using various flight control
parameters. Using the FADEC 80 will avoid the overrunning required
in prior art pitch control devices.
Accordingly, it will now be apparent that very low power electrical
signals can readily shift pilot valve sleeve 84. This controls
fluid flow in servo motor 14 to drive the latter in opposite
directions to generate the much higher forces necessary to position
the servo control valve (the reduced diameter section 51 of the
shaft 50) to correspondingly drive the pitch actuator 19. The
integral configuration of the double-acting servo motor 14 with its
opposed rods or shafts provide a high compact, lightweight,
economical pitch control.
While the present invention has been depicted and described by
reference to a particular embodiment in order to explain the
invention, no limitation upon the invention is implied by such
reference. It is understood that various modifications may be made
to the preferred embodiment without departing from the scope of the
invention. For instance, one skilled in the art would understand
that the invention is readily suitable for use with a double-acting
propeller pitch actuator rather than the single acting actuator 19
illustrated. The invention is intended to be limited only by the
spirit and scope of the appended claims.
* * * * *